Dense fluid spray cleaning process and apparatus

ABSTRACT

Diclosed is a dense fluid spray cleaning apparatus comprising a gas supply ( 3 ) for providing a predetermined amount of a gas to an enhanced joule-thompson condensation reactor ( 2 ) and for providing gas to a propellant generator ( 4 ), a premix chamber ( 6 ) for receiving a solid particulate from the enhanced joule thompson condensation reactor and heated gas from the propellant generator, and a mixing chamber ( 8 ) for receiving the solid particulate and the heated gas and producing a spray stream containing the solid particulate.

BACKGROUND OF INVENTION

[0001] Carbon dioxide exists as a low-density gas at standardtemperature and pressure conditions and possesses phase boundaries witha triple point (Solid-Liquid-Gas co-exist in equilibrium like a glass ofice cubes and water) and a critical point (Liquid-Gas have identicalmolar volumes). Through pressure or temperature modification, carbondioxide can be compressed into a dense gas state. The term ‘Dense PhaseCarbon Dioxide’ is used herein to describe all phases of carbon dioxide:liquid state, supercritical state, dense gas state, and solid-state.These states have densities that are within the range of liquid-like ornear-liquid substances.

[0002] Compressing carbon dioxide at a temperature below its criticaltemperature (C.T.) liquefies the gas at approximately 70 atm. Coolingliquid-state or gas-state carbon dioxide to its freezing point causes aphase transition into solid-state carbon dioxide. Compressing carbondioxide at or above its critical temperature and critical pressure(C.P.) also increases its density to a liquid-like state, however thereis a significant difference between compression below and above thecritical point.

[0003] Compressing carbon dioxide above its critical point does noteffect a phase change. In fact, carbon dioxide at a temperature at orabove 305 K (88 F.) cannot be liquefied at any pressure, yet the densityfor the gas may be liquid-like. At the critical point the density isapproximately 0.47 g/ml. At or above this point carbon dioxide is termeda supercritical fluid (SCF). Supercritical carbon dioxide can becompressed to a range of liquid-like densities, yet it will retain thediffusivity of a gas. Continued compression of supercritical carbondioxide causes continued increase in density, approaching that of itsliquid phase.

[0004] Solid-state carbon dioxide is useful for removing particulatesand trace organic residues from surfaces, using a process typicallycalled Snow Cleaning or Snow Departiculation. Similar to liquid andsupercritical fluid cleaning agents, solid-state carbon dioxide'scleaning power can also be described in both physical and chemicalterms. The process of snow departiculation can be described as a kineticenergy transfer process called “Linear Momentum Transfer” in accordancewith the following vector quantity:

P=MV, where

[0005] P—Linear Momentum of Solid Carbon Dioxide Particle or SurfaceParticle

[0006] M—Mass of Solid Carbon Dioxide Particle or Surface Particle

[0007] V—Velocity of Solid Carbon Dioxide Particle or Surface Particle

[0008] A stream of solid carbon dioxide particles having significantmass and velocity impact a stationary surface particle causing thesurface particle with a given mass to accelerate away from the surfaceto a given velocity in accordance with the following equation:

V _(sp)=(M _(cp) /M _(sp))V _(cp), where

[0009] V_(sp)—Velocity of Surface Particle

[0010] M_(cp)—Mass of Carbon Dioxide Particle

[0011] M_(sp)—Mass of Surface Particle

[0012] V_(cp)—Velocity of Carbon Dioxide Particle

[0013] The physical energy transferred during a snow departiculationprocess is usually sufficient to overcome strong electrostatic andintermolecular adhesive forces, commonly referred to as Van der Waal'sforces, that hold small particles to the surface.

[0014] The mechanism for the removal of trace organic films using snowis not fully understood, but has been postulated to be a combination ofmomentum transfer and a phase change of minute solid carbon dioxideparticles from solid-state to liquid-state (compression) and subsequentsolutioning of trace surface residues. According to the phase diagramfor carbon dioxide, a minimum impact compression of approximately 6 atm(88 psi) at 195 K is required to produce a liquid interphase. Energytransformations are possible other than the formation of a liquid phase,including particle fragmentation or shearing, gas phase transition(sublimation), and temperature rise in the solid (thermal energy) atimpact.

[0015] Solid carbon dioxide is being used in a number of commercialproduct cleaning applications to remove trace organic and inorganicresidues and particulates. Liquid carbon dioxide is rapidly expanded(joule-thompson expansion) through an orifice of a valve to form amixture of subcooled gas state and solid state carbon dioxide—referredto as “snow” or “dry ice”.

[0016] Solid carbon dioxide is applied in conventional applicatorsaccording to two types of applicators, described as Type I and Type IIsnow cleaning applicators as follows:

[0017] Type I Snow Applicator: Liquid carbon dioxide, stored in a highpressure bottle, is expanded from 850 psi at 298 K through a suitablenozzle into gas state (the propellant) and solid state carbon dioxide(the cleaning agent) and directed at a substrate. Conventional Type Iapplicators are commonly used in precision cleaning applications atclose proximity to a substrate and have relatively simple operation andlow-cost designs.

[0018] Type II Snow Applicator: Liquid carbon dioxide is first expandedinto solid carbon dioxide using a suitable “dry ice machine”, packedinto dry pellets of uniform size, or shaved into a powder, and then fedinto a spray apparatus using compressed air to propel the solid carbondioxide from a spray nozzle. The air and solid mixture impacts thesurface. A Type II applicator is typically used for cleaning large rigidstructures because of its more aggressive action at close proximity(i.e., for coating removal) and long-range particle cleaning action(large and hard snow pellets). However, Type II equipment andoperational costs are significantly higher than Type I systems.

[0019] Type I and Type II applicators include:

[0020] 1. Fixed position applicators

[0021] 2. Pistol grip applicators

[0022] Conventional applicators are designed to have a single spraypattern, with various interchangeable nozzle designs for differentsubstrates and surface cleaning applications. Type II designs can alsovary impact energy through control of compressed air pressure whereasType I designs cannot. Disadvantages associated with these mechanicaldesigns include:

[0023] 1. Fixed spray pattern.

[0024] 2. Non-interchangeability of applicator designs(fixed<->handheld<->robotic).

[0025] 3. Bulky configurations.

[0026] 4. Uncontrolled tribocharging (electrostatic buildup) ofnon-metallic substrates such as plastics.

[0027] 5. Rapid localized substrate cooling and subsequent deposition ofcontaminating residues.

[0028] 6. Ineffective deep hole cleaning.

[0029] 7. Expensive equipment costs.

[0030] Conventional snow cleaning applicators (Type I and II) sufferfrom the following disadvantages:

[0031] 1. Impact energy and the amount of snow particles available atthe surface decreases as the distance from the expansion valve to theapplicator nozzle increases. Type I applicators must have an expansionvalve located close to the nozzle and the nozzle must also be very closeto the substrate to effectively remove residues.

[0032] 2. Entrainment of ambient air which often contains moisture,particles, and other contaminating residues which condense onto surfaceswhich have been supercooled by the snow particle/gas stream.

[0033] 3. Externally applied environmental control measures such asheated air and particle control hinder the cleaning performance and areapplied so generally that localized condensation, particle entrapment,or tribocharging still occur. Conventional applications employmacro-environmental control (clean rooms, infrared heaters etc.)measures. Type I snow applicators cannot be used in relativelyuncontrolled environments.

[0034] 4. The process of expanding liquid carbon dioxide into solidstate and subsequent contact of solid state carbon dioxide with surfacescauses a phenomenon called tribocharging, whereas the solid carbondioxide (primary dielectric) builds electrostatic charge of up to 5 to15 mJ at 10 KV to 20 KV as it contacts a substrate (secondarydielectric). This type of electrical charge build-up can be extremelydamaging to microelectromechanical devices (or can induce latent ESDdefects) and will cause a departiculated surface to become an attractor(magnets) of airborne particles following snow cleaning operations.Electrostatic effects can be caused through direct contact of chargedsolid carbon dioxide particles with the substrate which causes adischarge event or current flow through the surface (direct discharge)or may be caused through electrostatic field exposure and subsequentcharging of the surface (induced charging).

[0035] 5. In many applications, spray cleaning is performed independentof and prior to operations such as microwelding, adhesive bonding andthermal curing and soldering. Moreover, following production operationssuch as CMP the substrate is wet with aqueous residues and must be driedprior to snow cleaning operations. A method and apparatus is needed toserve as an integrated simultaneous drying, cleaning and productiontool.

[0036] 6. Xenon flashlamp technology is used with solid carbon dioxide(Type II) to remove old paint from aircraft surfaces. This type oftechnology uses an intense UV radiation (not a laser) burst to pyrolizesubstrates which produces a large amount of heating radiation as aby-product. The pyrolized paint is swept away from the substrate using aflow of carbon dioxide pellets. This technology is large and bulky andcannot be used to precisely clean small parts commonly found in thesemiconductor, electrooptical and electronics markets. A precisioncoherent photon-based technique is needed to remove small contaminantsfrom intricate assemblies.

[0037] 7. In some applications, solid phase carbon dioxide chemistryrequires physicochemical modification to provide enhanced separation andsurface finishing capabilities. To date, no effective technique has beendemonstrated to accomplish this requirement.

[0038] 8. Type II applicators also suffer from being too aggressive(i.e., substrate damage), very noisy, bulky and too costly for mostprecision substrate cleaning applications.

[0039] 9. Conventional snow cleaning applicators do not lend themselvesto integration with production processes such as stamping, welding,bonding, curing and abrasive surface finishing operations because of theaforementioned problems discussed above.

[0040] Conventional snow cleaning processes do not have a method forreal-time analysis of cleaned surfaces to accept or reject a particularcleaning operation. This is especially advantageous for in-linecontinuous quality control monitoring of surface cleaning performance.

[0041] Conventional ESD Control Methods used with Solid Carbon Dioxide:

[0042] Air Ionization—air is ionized using a DC or AC ionizer that isthen flushed over an affected surface. The problem with this approach isthat flowing air induces contamination through introduction ofhumidified air and potential particles. Also ionizing air impingementrequires flooding the surfaces to be cleaned. This process can subtractfrom the cleaning energy. Moreover, the charges present within thestructure of the cleaning agent are not reduced effectively using thistechnique.

[0043] U.S. Pat. No. 5,409,418 proposes a nozzle-mounted secondary gasionizer which surrounds the snow stream with oppositely charged ionsduring impingement. U.S. Pat. No. 5,725,154 proposes neutralizingcharges during snow cleaning following each cleaning pulse with aseparate propellant gas neutralization pulse.

[0044] Most prior art suffers from these typical drawbacks:

[0045] Impossible to precisely control charges being delivered to asubstrate—each substrate and atmosphere is different.

[0046] The portion of a substrate being impacted by the sublimablecleaning agent is not affected by neutralizing ions—only thecircumference of the snow spray is affected.

[0047] Backside or nearby electrostatic charging due to electric fieldsis not affected by these techniques—electric fields pervade thematerials creating complexly charged surfaces.

[0048] Nuclear Ionization—the substrate is exposed to radioactiveparticles (alpha). This process is line-of-sight and very short range.Obstructions of the smallest variety will eliminate beneficialionization using this technique.

[0049] Fong '786, referenced herein, uses nuclear ionization to reduceaccumulated electrostatic charges contained on solid carbon dioxidestored and mixed within a storage hopper and prior to and duringdelivery into a high pressure feed line. Fong '786 suffers from all ofthe drawbacks cited above.

[0050] Grounding—the substrate in grounded to earth using a suitableresistor to bleed charges at an acceptable rate. The main problem withthis approach is that the electrostatic charge and electrical overstressare not effectively controlled on non-conductive substrates.

[0051] Antistatic Chemicals—this approach is the most effective onpreventing charge creation by the cleaning agent. However this methodtends to, by itself, become a source of chemical contamination withinthe cleaning process. To date no use of antistats within cryogeniccleaning agents is known

[0052] Moreover, in cleaning quartz lenses, as well as many othernon-conductive substrates it is difficult to control electrostaticcharging of the quartz substrate during sublimable spray cleaning.Flooding the surfaces with ionized air only works prior to and followingsnow cleaning. During snow cleaning, as much as 2000 volts ofelectricity of positive and negative charge can be created following thesnow-surface tribocharging contact event. Contaminants such as particlestend to move in relationship to thermal and electric fieldgradients—both of which are present in snow cleaning.

[0053] The backside of the quartz is typically opposite in charge(conservation of charge) during snow cleaning, therefore the particlesonce lifted from a front surface migrate around the substrate within athin-film of subcooled atmosphere and become attracted to the oppositelycharged surface on the backside. Quartz cannot be grounded and commonlyused antistatic chemical agents contained in the cryogenic cleaningagent would leave stains during cleaning.

[0054] A photoelectric effect has been advantageously employed indifferent arts for decades. In certain commercial ionizationapplications, the photoelectric effect is used to produce highlyenergetic photons from 0.13 to 0.41 nm (9.5 to 3 KeV) to ionize anatmosphere surrounding a substrate during a production process.

[0055] As such there is a present need to provide an alternative densefluid spray cleaning and separation apparatus and process whichovercomes the limitations of conventional dense fluid spray technologyand provides an environmentally-safe cleaning and finishing alternativesto organic solvents.

[0056] As such there is a present need to provide clean and effectiveelectrostatic control method during sublimable cleaning processes. Sinceelectrostatic charging is most prevalent in cryogenic cleaning such ascarbon dioxide, argon or liquid nitrogen blasting—a three-dimensionalionization method and device is needed to resolve electrostatic chargingeffects in complex substrates being cleaned, regardless of composition,shape and size.

SUMMARY OF THE INVENTION

[0057] There have been many patents issued, and in this decadeparticularly, for solid-phase cleaning devices and processes. Noneemploy a coaxial momentum transfer mechanism using thermal-propulsioncontrol of particle velocity and size described herein. Improved coaxialdense fluid spray cleaning processes and apparatuses have been developedand are described herein which greatly improve cleaning performance,operational characteristics, adaptability and versatility over U.S. Pat.No. 5,725,154 by the present. Most importantly, the present inventionsignificantly improves the performance of conversion of liquid phase CO2to solid phase and control of particle size and velocity.

[0058] The present invention provides the following new improvements(embodiments):

[0059] The present invention changes temperature and pressure of aninert optionally, ionizable propellant gas over a wide range oftemperatures from 70 F. to 300 F. and pressures from 30 psi to 10,000psi—this changes the physicochemical and kinetic characteristics of anenhanced snow particle mass generated within a condensor tube located atthe center of a coaxial delivery system. Particle size, density,apparent hardness and velocity of a stream of condensed carbon dioxidecan be precisely controlled by altering the temperature and pressure ofthe propellant in combination with altering the length of enhancedcondensation tube which supercools and condenses precisely injectedamounts of liquid carbon dioxide. An enhanced solid particle-gas mixtureis produced prior to combining with condensation tube and propellant gastube assemblies within a coaxial delivery line. A device called anEnhanced Joule-Thompson Condensation Reactor (EJTCR), containing acoiled or looped reaction tube having various lengths and diameters, isused to produce and densify a mixture of solid carbon dioxide particles(Enhanced Snow) from a source of purified liquid carbon dioxide. TheEJTCR loop is thermally insulated and grounded and is comprised ofvarious lengths and inside diameters of polyetheretherketone (PEEK)tubing. Because most of the condensation and sublimation heat transferoccurs within the EJTCR loop, the result is improved efficiency of theinitial condensation reaction process. A propellant stream comprisingpressurized, heated, inert and optionally ionized gas is produced in aseparate subsystem. Purified inert gases such as carbon dioxide(preferred), nitrogen and clean dry air are heated using an in-lineheater, filtered and ionized using an in-line DC ionizer assembly.

[0060] The two streams are first indirectly mixed (ion transfer and heattransfer) using various lengths, diameters and compositions of coaxialcondensation assemblies and then directly mixed (heat transfer andmomentum transfer) using various thrusting and mixing nozzle designs.

[0061] The efficiency, in relation to snow mass generated and cleaningenergy performed, of the present invention is increased substantiallyover conventional Type I snow cleaning designs. Moreover, the presentinvention produces excess heat remaining following transfer, mixing andspraying operations, in accordance with the Carnot equation, whichprovides simultaneous local environmental control through inerting andthermostatting phenomenon.

[0062] The present invention describes several new and improved coaxialconfigurations, including interchangeable condenser tube assemblies,co-solvent injection system, various nozzles, manipulator and pistolgrip.

[0063] The present invention further teaches a method of adding liquidand gas phase additives an enhanced condensation tube which are mixedand dispersed within the dense solid phase prior to injection and mixingwithin a nozzle. This provides improved physicochemical characteristicsof the resulting spray cleaning agent such as improved contaminantsolvency and lower tribocharging upon contact with a substrate.

[0064] The present invention provides a process and apparatus whichdestroys electrostatic charges generated through tribocharging viadirect contact of solid carbon dioxide particles to the substrate aswell as cool and heated gas movement over adjacent surfaces. Unlikeprior art approaches to this problem using gas delivered or radioactivesources of charged counter-ions, the present invention applies softx-ray radiation (photons) to the stream of snow particles and substratesimultaneously. The present invention is superior over prior art in thatelectrostatic charges are destroyed in transit, during contact at thesolid-solid interface and during sublimation at the surface.

[0065] The present invention teaches an improved cleaning and productiontool combining a semiconductor laser operating at the near-infraredregion. Using such as laser simultaneously with the present inventionprovides the following unique process capabilities:

[0066] 1. Thermal drying of substrates before, during and following snowcleaning.

[0067] 2. Superior spot heating during snow cleaning to assist withcontaminant separation (lower stiction).

[0068] 3. Post snow cleaning production adjunct operations such as alaser welding, thermal curing, and soldering.

[0069] This embodiment uses a low-cost diode laser operating in the nearinfrared at a wavelength of between 780 and 940 nm.

[0070] Another feature of the present invention is the combination of arelatively new analytical technique called Optically Stimulated ElectronEmission (OSEE) spectroscopy, also called photoelectron emission (PEE),with the present snow cleaning processes and apparatus. OSEE providesfor instantaneous feedback to a host computer controlling and applyingthe cleaning process. Real-time correlation between cleaning parameterstemperature, pressure, condensation tube length and contact time) andOSEE cleanliness can be established in-situ and used to verify surfacecleanliness following each cleaning operation.

[0071] Another aspect the present invention is the addition of solidabrasives to the propellant gas supply. Mixing solid abrasives with thedense snow mass provides an improved microabrasive finishing ofsubstrates—cryogenic microabrasive finishing. The snow spray embrittlessurface features such as burrs during simultaneous impingement ofabrasive snow additives. The surface features of the substrate becomeharder at a lower temperature than the subsurface—therefore surfacefinishing is aided through an increase in hardness (less rolling androunding of edges and burrs). Following this the spray is used to removeresidue dusts and residues from the finished substrate.

[0072] Finally, the present invention discloses a cleaning system andsystem software for utilizing the various examples described above in aclosed workcell using a centralized multi-axis programmable robotoperating in a circular workcell pattern and using various stationshaving increasing particle cleanliness. This embodiment teaches the useof various robot hand tools—pick and place tool in combination with acleaning tool, cleaning-laser tool, cleaning-inspection tool, orcleaning-ionization tool. Substrates are first picked up using a pickand place tool and moved from a dirty loading zone into a cleanerprocess zone. The robot then changes hand tools, placing the hand toolin a cleaning fixture for subsequent cleaning, and picks up any one ofseveral novel snow or snow-process robots tools. Following roboticcleaning and/or processing, the robot cleans the pick and place toolscritical surfaces, and replaces the cleaning tool with the newly cleanedpick and place tool. The cleaned substrate is picked up and placed in astill cleaner unload zone. The combination of a zoned workcell with aprogrammable robot, software and novel cleaning and cleaning-productiontools provides an economical, versatile and adaptable cleaning andproduction tool.

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] These and other objects and advantages of the present inventionwill be obvious to those of ordinary skill in the art after having readthe following detailed description of the preferred embodiments whichare illustrated in the various figures summarized below.

[0074]FIG. 1a is a block diagram illustrating a dense fluid spraycleaning apparatus including an EJTCR loop in accordance with theinvention.

[0075]FIG. 1b is a graph illustrating the relationship between particlesize of solid carbon dioxide and propellant gas temperature with aconstant supersonic thrusting pressure.

[0076]FIG. 1c is a graph illustrating the relationship between velocityof solid carbon dioxide particles and propellant gas temperature with aconstant supersonic thrusting pressure

[0077]FIG. 1d is a graph illustrating the relationship between solidcarbon dioxide particle relative hardness and length of condensationtube with a constant diameter.

[0078]FIG. 1e is a graph illustrating the relationship between velocityof condensed solid carbon dioxide-subcooled gas mixture and length ofcondensation tube with a constant diameter.

[0079]FIG. 1f is a diagram illustrating the difference betweenconversion of heat to work (velocity) produced by conventional devicesand a device in accordance with the present invention.

[0080]FIG. 1g is a graph comparing the difference between substratethermostatting and local ambient inerting phenomenon in conventionaldevices and a device in accordance with the present invention.

[0081]FIG. 1h is a diagram illustrating the cumulative effect producedby the present invention with respect to local environmental control ofsublimation heat management, ambient inerting and tribocharge control.

[0082]FIG. 1I is a diagram illustrating the effect upon local ambientatmosphere and substrate using conventional snow cleaning.

[0083]FIG. 1j is a graphical representation of the effect upon localambient atmosphere and substrate using conventional snow cleaning with asheath of inerting gas.

[0084]FIG. 1k is a graphical representation of the effect upon localambient atmosphere and substrate using the present invention.

[0085]FIG. 1l is a phase diagram showing effect on relative snow densityand generation efficiency with respect to EJTCR loop length anddiameter.

[0086]FIG. 2a is a schematic drawing of a dense fluid spray cleaningapparatus including an EJTCR loop in accordance with the invention.

[0087]FIG. 2b is a block diagram illustrating various embodiments of thepresent invention.

[0088]FIG. 3 is a cross-sectional view of a spray applicator for use inaccordance with the present invention.

[0089]FIG. 4 is a cross-sectional view of a hypersonic spray applicatorfor use in accordance with the present invention.

[0090]FIG. 5 is a cross-sectional view of an additive spray applicatorfor use in accordance with the present invention.

[0091]FIG. 6 is a cross-sectional and a front view of a conductive sprayapplicator for use in accordance with the present invention.

[0092]FIG. 7 is a cross-sectional and a front view of a fanned sprayapplicator for use in accordance with the present invention.

[0093]FIG. 8 is a schematic drawing of a multiple spray applicatorassembly for use in accordance with the present invention.

[0094]FIG. 9 is a partial cross-sectional view of a extensionmanipulator for use in accordance with a spray applicator.

[0095]FIG. 10 is a partial cross-sectional view of a handgun sprayapplicator for use in accordance with the present invention.

[0096]FIG. 11 is a schematic drawing illustrating a photoelectrongenerator integrated with an spray applicator for use in accordance withthe present invention.

[0097]FIG. 12 is a schematic drawing illustrating a diode laserintegrated with an exemplary spray applicator.

[0098]FIG. 13 is a schematic drawing illustrating both photoionizationand diode laser heating.

[0099]FIG. 14 is a top and side schematic drawing illustrating anenvironmentally controlled robotic cleaning and inspection workstationfor use in accordance with the present invention

[0100]FIG. 15 is a schematic drawing illustrating architecture forautomatically controlling a robotic substrate cleaning process,inspection process and associated environment using a computer/PLC andsoftware.

[0101]FIG. 16 is a schematic drawing illustrating a cryogenicmicroabrasive surface finishing apparatus and process in accordance withthe invention.

[0102]FIG. 17 is a schematic drawing illustrating use of dynamicpressure control during a substrate cleaning operation

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0103] The invention describes an improved adjunct separation mechanismwhich involves the formation of variable-geometry microscopic substancescalled “Snow Gels” comprised of trace organic surface residues (treatedas solvents or solutes) dispersed in solid phase carbon dioxideparticles (treated as a subcooled solvent-solute matrix). This mechanismis supported by solubility research performed by Myers and Prausnitz (M.N. Myers and J. M. Prausnitz, “Thermodynamics of Solid Carbon DioxideSolubility in Liquid Solvents”, Ind. Eng. Chem. Fund., 4, 209,1965) inwhich they treat solid carbon dioxide (solid-state xenon has also beenstudied) as a subcooled liquid to determine cohesive energy values.

[0104] Solid carbon dioxide possesses electron acceptor (Lewis Acid) andmolecular quadrapole moment properties which contribute to ahydrocarbon-like cohesion energy and complex forming ability withhydrocarbons. Solid carbon dioxide has a measured solubility parameterof between 23 MPa^(1/2) and 20 MPa^(1/2) in the temperature range of 140K to 200 K that is comparable to its liquid-state cohesive energy.Therefore, the removal of thin films of hydrocarbons using solid-statecarbon dioxide may occur through a liquid-subcooled liquid/particle masstransfer mechanism, whereas the Snow-Hydrocarbon interface is proposedto be the continuous formation and removal of a lyophilic crystallinegel or rigid colloid which I call a snow-gel. This mechanism is furthersupported by the fact that heavy metals are insoluble in liquid carbondioxide, but should form complexes or colloids with organic-like solidslike solid-phase carbon dioxide. Cleaning tests show a reduction inmetal ion contamination using solid phase cleaning.

[0105] The proposed compression-liquefaction mechanism may be anintermediate step of snow-gel formation, whereby the liquid-hydrocarbonis transformed instantaneously into a snow-gel particle through rapidevaporation and cooling. Research by Myers and Prausnitz confirms thesolubility of solid carbon dioxide with several hydrocarbon systems.Laboratory experiments confirm the formation of a stable gel-likesubstances with various mixtures of hydrocarbon liquids and solid carbond a schematic diagram illustrating a dense fluid spray cleaningapparatus including an enhanced joule-thompson condensation reactor(“EJTCR”) loop in accordance with the invention ioxide.

[0106] Referring to FIG. 1a., there is shown a block diagramillustrating a dense fluid spray cleaning apparatus in accordance withthe invention. The apparatus includes an (EJTCR) (2), a CO₂ supply (3),a spray nozzle, a thermal inert or thermal ionized gas (propellant)generator (4), a premix chamber (6), and a mixing chamber (8).

[0107] Small amounts of liquid carbon dioxide, preferably from about 5to about 200 lbs/hr, more preferably from about 10 to about 30 lbs/hr,is metered from the CO₂ supply (3) under a pressure of between 300 and1000 psi and at a temperature of between 0 F. and 85 F. and injectedthrough a spray nozzle into the EJTCR loop. The liquid carbon dioxideexpands rapidly into a mixture of approximately 50% solid and 50%subcooled gas immediately upon injection. Following this expansion, theresulting 50:50 solid:gas mixture is introduced into a thrust formingcavity having various geometries to produce a supersonic spray stream.

[0108] The EJTCR (2) comprises a coiled section of polyetheretherketone(PEEK) tubing (loop) which is overwrapped with a grounded conductiveshielding (Faraday Cage) such as a metal spring or metal foil andfurther overwrapped with a thermally insulative material such aspolyolefin. PEEK is a preferred loop material because it is highlyflexible, can withstand very high pressure and very low temperatures,and is a good thermal insulator.

[0109] In the present invention, the initial expansion is a “seeding”process. As the seed or slug of subcooled liquid and gas mixture travelsdown the length of the EJTCR loop, the gas is condensed or coagulatedinto solid and solid is compacted into a dense mass. The EJTCR loop hasan O.D. of from about {fraction (1/32)}″ to about ⅛″, preferably about{fraction (1/16)}″ and an ID of from about 0.0025″ to about 0.080″,preferably from about 0.02 to about 0.08″. The EJTCR loop diametercreates expansion of the gas which causes a temperature decrease. TheEJTCR loop has a length of from about 6″ to about 20 ft, preferably fromabout 4 ft to about 5 ft. The EJTCR loop length creates compressionthrough drag forces. The temperature decrease (decreasing with increasedloop length) is observed as a result of heat transfer from expanding gasmolecules—this results in a condensation of expanding gas into solidphase (kinetic energy is converted into potential energy). As themixture travels the length of the thermally insulated EJTCR loop, veryefficient heat transfer occurs. As such, the longer the EJTCR loop—themore efficient the coagulation process. Moreover, increasing the lengthof the EJTCR loop increases pressure and drag within the loop—causingthe solid particles to pack together into a dense solid carbon dioxidemass.

[0110] Microdroplets of liquid carbon dioxide are caused to shear underturbulent conditions (Reynolds Number>10,000) within the EJTCR loop.Gas-particle velocity decreases and turbulent shear increases over thedistance of the loop. The longer the loop—the higher the turbulentshear. This increase in shear increases coagulation of liquid and gasphases into solid phase by contacting vapor within the loop with newlyformed solid particles having a temperature that is below the saturationtemperature. Heat transfer within the loop is a combination of twomodes—conduction and convection. The enhanced condensation processinvolves mass transfer simultaneous with heat transfer. The EJTCR loopmaintains high pressure and low temperature over along distance (time).Increasing pressure, decreasing temperature and increasing time enhancethe condensation process. The net result of the EJTCR process is anefficient and controllable conversion of liquid carbon dioxide into arelatively slow moving dense solid mass of carbon dioxideparticles—called enhanced snow. Increasing the loop length for a givenloop internal tube diameter increases conversion. The purpose ofwrapping the loop with grounded electrical shielding is to drain awayelectrostatic charges generated during the coagulation process andmovement of this dielectric mixture through the EJTCR loop. Anadditional overwrap of thermal insulation on the loop prohibits heattransfer from the ambient atmosphere which would be detrimental toparticle growth.

[0111] A thermal inert or thermal inert ionized propellant gas generator(4) provides a source of propellant gas. Suitable propellant gasesinclude carbon dioxide, nitrogen or clean dry air or other gases whichcan be purified, filtered, heated and optionally ionized. The preferredpropellant gas is carbon dioxide. The propellant gas is used herein notonly as a propellant, but simultaneously as a solid particle sizemodifier, ion neutralizer, inerting agent, and thermostat agent. In someembodiments the gas generator includes an in-line ionizer for ionizingthe propellant gas to produce positive and negatively charged gasmolecules. This mixture of charged gas molecules is used to bathe thesnow tube and propellant gas tube assemblies within premixchamber—neutralizing charges created by the movement of dielectric gasand solids within each tube. An alternative design uses a grounded metalcage to drain away charges generated. A benefit of using the in-lineionizer is that the present invention can be used to spray thermalionized gas on a substrate following cleaning to insure that no residualelectrostatic charges are left behind following cleaning which mightattract airborne particles.

[0112] The premix chamber (6) is a section where the propellant gas isindirectly contacted with the enhanced snow from the EJTCR. Thepropellant gas is caused to flow over a predetermined length of flexible(PEEK) or rigid (stainless steel) inner tube, the snow tube, carryingthe enhanced snow. The propellant gas is carried in an outer coaxialtube, the propellant gas tube, which itself is either flexible (Teflon)or rigid (stainless steel. The coaxial premix chamber transfers heat,and optionally ions, under controlled conditions from the propellant gasto the enhanced snow. Changing the type of premix snow tube from PEEK tostainless increases heat conduction. Heat contained in the propellantgas slowly diffuses through the snow tube and is transferred to theenhanced snow. This causes the enhanced snow to sublimate. Increasingthe heat content of the propellant gas and increasing the contact time(length of premix chamber) increases the sublimation. As such, theenhanced snow is expanded and accelerated towards the end of the snowtube. It has been discovered that heating the snow tube greatly improvessnow particle flow from the EJTCR and up to the mixing chamber. Withoutwishing to be bound by a theory of operation, it is believed that a thinlaminar high velocity carbon dioxide gas sheath is produced between thesnow particles and the inner wall of the PEEK or stainless tube wall.This is analogous to lubrication and prevents the dense snow particlesfrom packing, clogging and spitting from the snow tube. There is asignificant difference in snow tube flow characteristics with andwithout the presence of propellant gas flow. Moreover, heat transferthrough the snow tube initiates the process of solid particle sizereduction and provides an initial impulse to the mixture prior toinjection into the mixing chamber.

[0113] The propellant gas and enhanced snow are combined in the mixingchamber (8) to produce a composite supersonic spray stream. The mixingchamber includes a nozzle wherein the inner snow tube is fed into amixing section of a convergent-divergent mixing nozzle. The propellantgas is compressed through the convergent section that increases pressureand reduces velocity, mixed with the enhanced snow particles andexpanded through a divergent section wherein the pressure of the mixtureis reduced which causes the mixture to rapidly accelerate out of themixing chamber. The heat content of the propellant gas generates asignificant impulse from sublimating the dense enhanced snow mass.Depending upon the nature of the mixing nozzle, different impulse andspraying patterns can be produced. Depending upon the temperature andpressure of the propellant gas, a variety of particle size ranges can beproduced and the resultant mixture(10), has a much higher energy contentthan those produced using conventional snow spraying devices.

[0114] Having discussed in general the basic operation andcharacteristics of the present invention, following is a detaileddiscussion of each core component and adjunct systems and processes thatcontrol and optimize the present invention.

[0115]1 b illustrates the relationship between particle size of solidcarbon dioxide and propellant gas temperature with a constant supersonicthrusting pressure. By varying the temperature of a propellant gas and(1) first indirectly contacting propellant gas with the enhanced snowthrough a thin heat transfer wall (Premixing heat and ions) and then (2)directly mixing the propellant gas with the enhanced snow particlemass—the average solid carbon dioxide particle size of the resultingspray stream can be altered considerably. The particle size can bevaried over a wide range from 100 micrometers (12) to 0.2 micrometers(14) by varying the temperature of the propellant gas from 70 F. to 300F. This variance is relatively constant for a fixed propellant pressure,fixed EJTCR loop length and inner diameter and premix distance.

[0116]FIG. 1c illustrates the relationship between velocity of solidcarbon dioxide particles and propellant gas temperature with a constantsupersonic thrusting pressure. By varying the temperature of apropellant gas and (1) first indirectly contacting propellant gas withthe enhanced snow through a thin heat transfer wall (Premixing heat andions) and then (2) directly mixing the propellant gas with the enhancedsnow particle mass—the average solid carbon dioxide particle velocity ofthe resulting spray stream can be altered considerably. The particlevelocity can be varied over a wide range from less than 500 ft/sec (16)to greater than 1600 ft./sec (18) by varying the temperature of thepropellant gas from 70 F. to 300 F. This variance is relatively constantfor a fixed propellant pressure, fixed EJTCR loop length and innerdiameter and premix distance.

[0117]FIG. 1d is a graph illustrating the relationship between solidcarbon dioxide particle relative hardness and length of condensationtube with a constant diameter. By varying the length of the EJTCRloop—the relative density (d=p/97.6) of the solid carbon dioxideparticles stream contained within the snow tube can be alteredconsiderably. The relative density can be varied over a wide range from0.5 g/cm3 (20) to approaching 1 g/cm3 (22) by varying the length of theEJTCR loop from 0.1 meters to 10 meters. This variance is relativelyconstant for a fixed diameter of thermally insulated PEEK condensationtube.

[0118]FIG. 1e is a graph illustrating the relationship between velocityof condensed solid carbon dioxide-subcooled gas mixture and length ofcondensation tube with a constant diameter. By varying the length of theEJTCR loop—the velocity of the enhanced solid carbon dioxide particlesstream contained within the snow tube can be altered considerably. Thevelocity is varied over a wide range from 600 ft/sec (24) to approaching50 ft/sec (26) by varying the length of the EJTCR loop from 0.1 metersto 10 meters. This variance is relatively constant for a fixed diameterof thermally insulated PEEK condensation tube.

[0119]FIG. 1f is a diagram illustrating the difference betweenconversion of heat to work (velocity) produced by conventional devicesand a device in accordance with the present invention. By varying thetemperatures of mixing of the propellant gas having variable pressureand high temperature with an enhanced snow particle stream having highdensity and low temperature, and where the propellant gas velocity issupersonic and the enhanced snow stream velocity is subsonic—the CarnotEfficiency (E—work performed), expressed as E=Tmax−Tmin/Tmax, can bealtered over a range of efficiencies and results in a much improved Eover conventional snow spray streams. The E can be varied over a widerange from 30% (28) to greater than 50% (30) by varying the temperatureof the propellant gas from 70 F. to 300 F. This variance is relativelyconstant for a fixed diameter of thermally insulated PEEK condensationtube, premix chamber and propellant gas pressure. By contrast,conventional snow streams have a calculated E of between 5% (32) and 30%(28). The work performed in the present invention is expressed asimpulse, thrust or propulsion (34). The residual heat of the propellantgas, expressed as heat not converted into work (1-CE), is used in thepresent invention for in-situ ambient inerting and thermostatting at ornear the substrate during impact of supersonic snow particles (36).

[0120] By contrast, conventional snow sprays produce a 50:50 mixture ofvery cold solid and gas. The gas in this conventional approach is alsothe solid propulsion agent—however its temperature is near thesaturation temperature. As a result, this gas produces undesirableenvironmental effects such as ambient inclusion and condensation ofmoisture and rapid freezing of the substrate.

[0121]FIG. 1g is a graph comparing the difference between substratethermostatting and local ambient inerting phenomenon in conventionaldevices and a device in accordance with the present invention. Theresultant temperature of a composite spray used in the present inventionis much higher and is variable as compared to conventional snow spraystreams. To demonstrate the thermostatting characteristics of thepresent invention, a measurement of average surface temperature duringnormal scan spraying (1 inch/sec) a 4 inch by 4 inch (16 in2) aluminumplate using a conventional snow gun (Va-Trans-SnoGun) and the presentinvention shows the various thermal profiles produced over time. Aconventional snow spray gun produces an average surface temperature of−20 F. after 10 seconds of scan spray (38) and almost instantaneouslymoisture is condensed on the substrate. By contrast spraying using thepresent invention produces a different thermal profile for eachsuccessive increase in temperature—150 F. (40), 200 F. (42) and 250 F.(44). Although the sprayed surface temperature of the substrate droppedbelow the ambient dew point (46)—there was no visible condensation onthe substrate. This is due to the local inerting characteristics andphenomenon associated with the present invention.

[0122]FIG. 1h is a diagram illustrating the cumulative effect producedby the present invention with respect to local environmental control ofsublimation heat management, ambient inerting and tribocharge control.The propellant gas used in the present invention is used uniquely as adynamic particle size control agent, ion transfer agent, propulsionagent, thermostatting and inerting agent. By controlling propellant gastemperature, flowrate and pressure, the local environment above and onthe surface being cleaned is controlled. Environmental controlcharacteristics include simultaneously supplying heat to sublimatingsolid particles upon impact (sublimation heat energy—thermostatting) andexcluding the ambient atmosphere from the area being cleaned (inerting).

[0123] Referring to FIGS. 1i, 1 j and 1 k, the environmental controlbenefits provided by the present invention are illustrated by comparingconventional snow cleaning methods and devices to the present invention.FIG. 1i shows the environmental dynamics of a simple conventional snowspray device. An extremely cold stream of solid and gaseous carbondioxide (48) is directed at a substrate (50). Two undesireablephenomenons occur simultaneously. First, the ambient atmosphere (52)which surrounds the spray stream (48) and which contains particle,moisture and hydrocarbon contamination is condensed into the cold spraystream (48). Once incorporated into the stream, the contaminants areimmediately deposited onto the substrate (50). A second undesirableeffect is heat transfer from the substrate. Because the conventionalsnow stream is very cold, upon impact the cleaning spray sublimates andextracts significant heat (54) from the surface. The surface must beheated continuously from below or above to compensate for thissublimation heat energy.

[0124]FIG. 1j shows the environmental dynamics of a simple conventionalsnow spray device with a shroud of heating gas (called sheath flow). Anextremely cold stream of solid and gaseous carbon dioxide (56) isdirected at a substrate (58) with a sheath flow of inert gas flowingconcentrically about the snow stream (60). In this application, ambientatmosphere (62) is excluded from the center of the cleaning zone. Theundesirable effect here is the same as a simple conventional snow sprayoperation—heat is transferred from the substrate. Because the centerstream is a conventional snow stream and is very cold, upon impact thecleaning spray sublimates and extracts significant heat (64) from thesurface. The surface must be heated continuously from below or above tocompensate for this sublimation heat energy or the sheath flow mustremain on for some period of time following the snow cleaningspray—operating in a pulse mode.

[0125]FIG. 1k shows the environmental dynamics of the present invention.An extremely cold stream of solid and gaseous carbon dioxide is mixedwith superheated gas to produce the stream (66) which is directed at asubstrate (70). In the present invention, ambient atmosphere (72) isexcluded from the center of the cleaning zone and, unlike conventionalapproaches, heat (74) is transferred to the surface of the substrate.Because stream contains residual heat, it is expanding from the centralcleaning zone and excludes the ambient environment. Additionally, whenthe entrained snow particles sublimate at the surface, heat (74) isextracted preferentially from the surrounding component around, aboveand at the surface of the substrate. The present invention packagessublimation heat and delivers it with the solid snow particle. Theresult is that the surface does not have to be heated continuously frombelow or above using external heat sources to compensate for thissublimation heat energy and separate inerting atmospheres do not have tobe incorporated.

[0126]FIG. 1l shows the overall relationship between the EJTCR looplength and internal pressure with respect to the generation of a densemass of solid carbon dioxide in relationship to pressure and temperatureconditions on the carbon dioxide phase diagram. Referring to the figure,during expansion from gas-saturated liquid phase (A) a conventional snowcleaning nozzle produces a cleaning mixture (B) comprising a maximum of50% solids and 50% cold vapor. Conventional snow spray cleaning mixturestend to be very porous following expansion because the microscopic sizedsolid particles rapidly sublimate upon exposure to ambient conditions oftemperature and pressure. Conventional snow sprays are controlledthrough the use of convergent-divergent nozzle designs

[0127] By contrast, in accordance with the inventive device, a smallquantity of gas saturated liquid is injected into a long thermallyisolated and electrically grounded loop (called the EJTCR Loop herein)to produce a controlled dense mass of predominantly solid carbon dioxide(C). The EJTCR snow (called enhanced snow herein) generation process isdirectly controlled through loop length and diameter. For a fixedinternal diameter of between 0.007 inches and 0.080 inches and varyingthe length of the loop from 0.1 to 10 meters (expansion volume from 5 ulto 30 milliliters), various relative densities of snow mass as describedabove can be produced. In general, for a fixed internal diameter and byelongating the expansion loop—variable densities can be produced. Asshown in the Fig., long EJTCR loops result in a lower internal looptemperature and higher internal loop pressure—both favor solidsgeneration.

[0128] The following is a more detailed description of an exemplaryapparatus for performing the present invention based upon the above corestructure.

[0129] Referring to FIG. 2a, a supply of carbon dioxide gas (76) isconnected to a tee (78) which splits the gas stream into two highpressure gaseous streams. The carbon dioxide gas supply is derived froma supply of gas saturated liquid (80) held under a pressure of between300 psi and 1000 psi and a temperature of between 0 F. and 85 F. A pipe(82) feeds one fraction of the high pressure gas to a regulator (84)which is controlled using a pressure controller (86) and pressure sensor(88). Regulated carbon dioxide gas feeds from the regulator (84) via afeed line (90) into a valve (92). The valve (92) is connected via a feedline (94) which feeds pressure regulated carbon dioxide gas into aheater assembly (96). The heater assembly (96) comprises a temperaturecontroller (98) and temperature sensor (100). The heater assembly (96)heats the pressure regulated carbon dioxide gas which feeds pressureregulated and heated carbon dioxide gas via feed line (102) into aparticle filter assembly (104). The pressure regulated, heated andfiltered carbon dioxide gas is fed via feed line (105) into an optionalionizer assembly (106) to create thermal ionized or thermal inert carbondioxide gas. The optional ionizer assembly (106) comprises a tee. (notshown) containing an electrode (not shown) which is connected to powersupply (108) which generates both positive and negative potential on theelectrode. Pressure regulated, heated, filtered and optionally ionizedcarbon dioxide gas is fed via feed line (110) into a coaxial premixchamber (112).

[0130] A second fraction of unregulated high pressure carbon dioxide gasis fed via feed line (114) into catalytic purifier (116), available fromM.O.S.T, Wisconsin. The unregulated high pressure and catalytic purifiedgas is fed via feed line (118) into a condenser unit (120) whereupon itis condensed, via heat transfer or pressure pump, from a gas phase intoa liquid phase. In an alternative embodiment, not shown, the purifiedgas exiting the catalytic purifier (120) is further split into twostreams—providing an ultrapure propellant gas supply for practicing thepresent invention. The purified liquid carbon dioxide is collectedthrough condensing line (122) into a stainless steel reservoir (124).Purified liquid carbon dioxide is transferred via feed line (126) to amicrometering valve (128), which controls the feedrate through valve(130). Liquid carbon dioxide is fed from valve (130) via feed line (132)and through an in-line particle filter (134) into an enhancedjoule-thompson condensation reactor (EJTCR) loop (136). The EJTCR loopmay be constructed of various lengths and internal diameters of coiledPEEK tubing, which are coiled, wrapped in electrically conductive andgrounded (138) shielding (not shown) and overwrapped in a suitablethermal insulation such as polyolefin shrink tubing (not shown). The endof the EJTCR loop is fed into and down the center of premix chamber(112) serving as a flexible inner snow tube (142) up to the mixingchamber (144). Optionally, the end of the EJTCR loop may be integratedto the beginning of the premix chamber (112) using a suitable connector(140) to change the PEEK connection into a rigid polished stainlesssteel snow tube (142).

[0131] The premix chamber (112) comprises an outer flexible or rigidpropellant gas line (146) housing a centrally located flexible or rigidsnow tube (142). The snow tube (142) may be wrapped in a groundedmetallic shielding (not shown) to dissipate electrostatic charges fromsolid carbon dioxide flowing within the snow tube (142) and propellantgas flowing within the propellant gas tube (146). Alternatively, thepropellant gas tube (146) may be wrapped in a grounded metallicshielding to provide beneficial electrostatic charge control. Thepropellant gas tube (146) is connected to the mixing chamber (144)wherein the snow tube (142) is inserted into the center of the mixingchamber (144).

[0132] The mixing chamber (144) comprises a convergent-divergent nozzleconfiguration wherein the snow tube (142) may be positioned to be withinany position from the divergent section (148), the mixing section (150),or the divergent section (152) of the mixing chamber (144). Positioningthe snow before the convergent section or after the divergent sectioncauses the stream to be highly turbulent and unpatterned. The preferredposition for the snow tube is within the mixing section (150) whereinstructural changes can be made to both the convergent and divergentsections to optimize the pattern and thrusting of the. An example of adynamically adjustable nozzle configuration is given in U.S. Pat. No.,154, which patent is herein incorporated by reference.

[0133] Two basic sensors are used to determine if 1) carbon dioxidesupply problems exist and 2) purification system problems exist. Apressure sensor (152) located on the carbon dioxide gas supply line(154) and feeding the tee (78) is used to determine if the gaseoussupply is depleted. An optical liquid level sensor (156) connected tothe purified liquid carbon dioxide reservoir (124) determines if liquidis being condensed within the condenser unit (120).

[0134] Some embodiments additional include an injection system forincorporating additives. For example additives can be included into theliquid carbon dioxide stream. A purified liquid carbon dioxide additiveinjection system includes a source of additive (158) connected to thepurified liquid carbon dioxide reservoir via an injection pump (160).

[0135] In other embodiments, an additive injection system (162) isintegrated following the EJTCR loop using a tee (164). Suitableadditives at this connection point also include alcohols, surfactants,gases, and the like. In still other embodiments, an additive injectionsystem (166) is integrated into the mixing chamber (144) using a tee(168). Finally, an additive injection system (170) may be integratedinto the propellant gas tube (146) using a suitable connection tee(172). Suitable additives at this connection point include alcohols,surfactants, gases, and the like.

[0136] Basic control systems for the present invention are alsoillustrated in FIG. 2a. Propellant gas pressure may be dynamicallychanged over time using a digital or analog input (174) to the pressurecontroller (86). Propellant gas temperature may be changed over timeusing a digital or analog input (176) into the propellant gastemperature controller (98). Similarly, the manual micrometering valve(128) may be replaced with a dome-loaded digital metering valve. Anelectronic switch (178) is provided to turn the optional propellant gasionizer on and off. An electronic switch (180) is provided to turn onthe flow of regulated carbon dioxide into the heater assembly (96). Anelectronic switch (182) is provided to turn on and off the injection ofmetered purified liquid carbon dioxide into the EJTCR loop (136) throughthe filter assembly (134). Finally, an electronic switch (184) isprovided to the additive injection pump (160).

[0137] An additional embodiment of the present invention includes amethod for preventing and eliminating electrostatic charges generatedduring contact of snow, with the substrate. Shown in FIG. 2a is aphotoionizer (186) which is electronically turned on and off using anelectronic switch (188). This embodiment directs photoelectrons at thecleaning target area, bathing the spray and substrate with ionizingphotoelectrons. The photoelectrons ionize multiple interphases—gas-gas,solid-gas and solid-solid, destroying unbalanced electric chargesin-situ and during creation.

[0138] Another embodiment of the present invention includes a diodelaser (190) which is turned on and off using an electronic switch (192)and power controlled using a digitally controlled power supply (notshown). The diode laser provides coherent heating radiation to a spot(cleaning target) which is used in the present invention to enhancecleaning and serves as a combination of cleaning, welding, thermalcuring and drilling tools.

[0139] Still another embodiment of the present invention includes asurface analysis device, such as an ultraviolet photoemission analyzer,to provide in-situ feed-back and control of the cleaning process. Anultraviolet radiation optically stimulated electron emission sensorprovides surface cleanliness data which can be dynamically correlated tothe various control parameters—pressure, temperature, snow injectionrate and time. This capability provides an in-situ means of calibratingand validating the cleaning process. As shown in FIG. 2a, an OSEE sensor(194) is coupled to an on/off switch (196) and integrated with aspectroscopic analyzer (not shown) which provides feedback throughsoftware to the process control software.

[0140]FIG. 2b is a block diagram illustrating various embodiments of thepresent invention. This figure shows the EJTCR (198), the ThermalInert/Ionized Gas Propellant Generator (200), the Premix Chamber (202)and the Mixing Chamber (204), along with a Photoionization System (206),a Diode Laser System (208), an Optically Stimulated Electron EmissionAnalyzer (210), a Multi-axis programmable robot system (212), a roboticenvironmental control system (214) and computer software (216).

[0141]FIG. 3 shows an economical mixing applicator comprising threeintegrated components. The first component comprises a nozzle (218)having a rear threaded male section with a propellant tube sleeve (220)and a front convergent-divergent mixing nozzle (222). The secondcomponent is a propellant tube connection sleeve (224) having a threadedfemale connection and an elongated and tapered inner sleeve (228). Thethird component is the premix chamber comprising a flexible or rigidpropellant tube (230) and a flexible or rigid Snow Tube (232). Assemblyof the three components is shown in the figure and described as follows:The propellant tube (230) is pushed over the propellant tube sleeve onthe mixing nozzle and located rear of the threaded section (220). Theconnection sleeve (224) is slid over the propellant gas tube andthreaded to the mating male threaded section (220) of the mixing nozzle.This action causes the connection sleeve inner tapered wall (228) tocompress over and grip the outside of the propellant gas tube. The SnowTube (232) is slid into the center of the coaxial assembly andpositioned within the mixing section (234) of the mixing nozzle (218).Once positioned within the mixing nozzle, the Snow Tube (232) iscompressed using a suitable fitting at the entrance of the PremixChamber (FIG. 2a, 140) to maintain its position.

[0142]FIG. 4 illustrates a hypersonic spray applicator for use with thepresent invention. This nozzle is designed for use with propellant gaspressures of between 100 psi to 5000 psi or more to produce thehypersonic spray. It is constructed of stainless steel and contains atee section (236) wherein the PEEK Snow Tube (238), comprising the endof the EJTCR loop, is brought into and sealed to the tee section andmated to a section of stainless steel Snow Tube (240) using a pair ofbulkhead compression fittings (242). High pressure propellant gas is fedinto the tee (244) from the propellant gas generator (not shown). Thebody of the hypersonic spray applicator is grounded (246).

[0143]FIG. 5. illustrates an additive injection apparatus for use withthe present invention. The propellant gas nozzle contains a small bore(248) extending through and into the entrance of the mixing section(250), at a 45 degree angled bore, through which a small PEEK orstainless steel injection needle (252) is inserted. During sprayingoperations, small amounts of liquids or gases are fed through the needle(252) into the mixing chamber.

[0144]FIG. 6. illustrates a conductive brush cleaning apparatus for usewith the present invention. The nozzle contains conductive nylonbristles (254) concentrically positioned about the exit of an extendedlength mixing section (256). During spray cleaning operations, the brushassembly aids in dislodging large particles and residues whilemaintaining a ground through the spray applicator body (258).

[0145]FIG. 7 illustrates a fan spray cleaning apparatus for use with thepresent invention. The nozzle contains elongated and flattened divergentsection (260) through which the stream is sprayed.

[0146]FIG. 8. depicts a multiplexed spray assembly. PEEK tees (262) areused to split the enhanced snow stream fed from the EJTCR loop (264)into four individual Snow Tubes (266) which are fed into a multiportedmanifold (268) using a bulkhead compression fitting (270). Affixed tothe manifold are four mixing nozzles (272) through which the Snow Tubeis fed into the mixing sections. Propellant gas is fed into the manifoldthrough a common port (274). Any number of spray heads can be developedas long as the feed diameter from the EJTCR loop is sized to provide anadequate feedrate through the individual snow tubes. The multiportedspray applicator is useful for robotic and machine integrationapplications and produces a large cleaning pattern with only a smallamount of movement in any direction (276).

[0147]FIG. 9 illustrates spray manipulator assembly for extending thespray applicator into hard to reach areas. The device comprises anadjustable mounting head (278), extension or telescoping shaft (280),and handle (282) with actuation trigger switch (284) and optionalpropellant gas (ionization) trigger switch (286). The manipulator isintegrated with the generator through a flexible coaxial assembly (286).

[0148]FIG. 10. Illustrates a spray handgun assembly for manually holdingand using the spray applicator. The assembly comprises a body (288)through which the spray applicator (290) is fed into and clamped. Thehandgun body contains a actuation trigger switch (292) and optionalpropellant gas (ionization) trigger switch (294). The handgun assemblyis integrated with the generator through a flexible coaxial assembly(296).

[0149]FIG. 11 illustrates a photoionizer integrated with the applicator.As shown in the figure, the photoionizer (298) and spray applicator(300) are mounted on a common manifold (302). The manifold (302)contains a photoionizer pivot (304) and spray applicator pivot (306) foradjusting the alignment of each device with respect to the contactcleaning point on the substrate (308). The photon-cleaning manifold isconnected to a multi-axis robot (not shown) using a robotic mount (310).Connecting the manifold to a multiaxis robot provides for any number ofpossible orientations and angles. The photoionizer is tunable to provideboth spot and broad-spectrum substrate ionization—the robot provides thefocusing control for both the spray applicator and photoionizer. Anotherfeature shown in the figure is a spin processor (312). The spinprocessor holds the substrate under vacuum (314) via a vacuum chuck(316). The substrate is spun at a rotational velocity of between 20 and5000 rpm. The photon-cleaning manifold is scanned from the interior (asshown) to the perimeter of the substrate while the substrate is spinningbelow. Software is used to control the pressure, temperature andphotoionization process sequencing. In some embodiments the propellantgas pressure is decreased while the manifold moves from the interiorregion (lowest centripetal force) to the perimeter (highest centripetalforce). Using this approach, the actual impact force (cleaning energy)of the particle stream is continuously decreased to compensate for theincreasing centripetal force toward the perimeter -providing consistentcleaning energy across the entire substrate. Another feature is theability to defocus the photoionizer to provide entire substrateionization following cleaning and focused ionization during spraying toprovide intense localized ionization. Finally, the photon-process isperformed in a soft x-ray shielding box (318) to protect workers fromexposure. X-Ray shielding can be most materials of suitable photonabsorbing thickness such as 0.250 inch static safe clear acrylic.

[0150] The traditional ionization method uses air to deliver ions to anaffected substrate. However this only works as a line-of-sight solutionand the mechanics of cryogenic spray cleaning eliminates mostline-of-sight ionization opportunities. In solid carbon dioxide spraycleaning, five tribocharging interfaces are present:

[0151] Interface 1: snow particle—snow particle

[0152] Interface 2: snow particle—gas molecules

[0153] Interface 3: substrate surface—snow particle

[0154] Interface 4: substrate surface—gas molecules

[0155] Interface 5: gas molecules—gas molecules

[0156] Moreover, these tribocharging interfaces are three-dimensionaland comprise various phases of matter—solids, liquids (condensed vaporsand contaminants) and gases. Conventional ionization techniques manageone of two of the interfaces at best and do not manage all dimensionsand phases present. For example in air ionization—the contacted surfaceis affected only and requires time to deliver the ions in sufficientconcentration to neutralize electrostatic charges. In this example, theatmosphere above and down to the substrate is only affected. The snowstream, snow stream-substrate and backside interfaces of the substrateare not affected by air ionization. Grounding of non-conductors does notwork.

[0157] Furthermore, as noted above, the cleaning of non-conductors withsolid carbon dioxide produces many undesirable electrostaticeffects—non-conducting substrates being cleaned charge unevenly withpockets of positive and negative charge, the solid carbon dioxide-gasparticle mix is significantly charged prior to delivery to thesubstrate, the ensuing vapor cloud is highly charged. This also includesconductors which are ungrounded. All of these electrostatic events areoccurring simultaneously during solid carbon dioxide spray cleaningoperations. To date, the traditional techniques have been implemented,with the above-mentioned negative consequences. These problems areovercome by the inventive embodiments which provide a method and devicefor cleaning ESD/EOS sensitive electronic devices with sublimablecleaning agents, and more specifically solid carbon dioxide, withoutproducing undesirable ESD.

[0158] Benefits of Combining Photons and Solid Carbon Dioxide:

[0159] Heretofore, photoionization has not been implemented in snowcleaning. This may be due to its cost and potential safety issuesassociated with soft x-ray radiation. Regardless, this has resulted inthose skilled in the art not investigating the benefits of using x-raysin combination with solid-phase carbon dioxide during cleaning orcooling applications. This researcher has investigated thephotoelectric-carbon dioxide combination and reports the following andpreviously undiscovered benefits of this unique combination:

[0160] 1) Photoelectrons pass directly into and through the cryogenicsolid spray matrix-creating ions in-situ through ionization of thegaseous carbon dioxide gas surrounding solid carbon dioxide particles.This effectively eliminates charge build-up during transport from thenozzle to the substrate.

[0161] 2) Photoelectrons pass through substrate creating ions on thefront surface (surface being cleaned) and back surface (surface notbeing cleaned). This prevents contaminants from passing around thesubstrate and sticking to the backside (a.k.a. electrostatic flypapereffect) during cleaning.

[0162] 3) Photoelectrons pass through the atmosphere between thecleaning applicator and substrate and behind the substrate creating avirtual pool of ions within the carbon dioxide atmosphere, substrate andsnow simultaneously. This eliminates charge build-up within theatmosphere contacting the substrate.

[0163] 4) Unlike air ionization, the photoelectric ionization effect isenhanced by the motion of gas molecules within the photon beam. This isvery beneficial since the solid carbon dioxide spray technique producesa very turbulent atmosphere.

[0164] 5) The photoionization effect is 3-dimensional and is noteffected by phases present, gas flow, temperature and humidity. Thesolid carbon dioxide-substrate-atmospheric system is fairly invisible tothe photons and therefore do not hinder the ionization effect.

[0165] 6) The photoionization effect works instantaneously upon thesubmicron particles held on surfaces, delivering significant energy tothe surface-particle region—breaking strong electrostatic energy bondsinstantly.

[0166] 7) During application of snow particles—the contact interfacewhere the particle meets the substrate is continuously bombarded withionizing radiation (the radiation passes through the snow particle).This eliminates the tribocharging effect during creation. This providesa photoelectric antistatic agent at the solid particle-substrateinterface without chemical contamination.

[0167] 8) The photoionization effect with the device can be tuned towork on all shapes, sizes and compositions of substrates—thephotoionizer produces a 120 degree cone of ionization. The closer thephotoionizer, the more focused and faster the ionization effect (higherdensity of photons). During sublimable spray operations, thephotoionizer is focused (small area radiation) primarily on the contactzone. During pre- and post-cleaning operations, the photoionizer is in adefocused (large area radiation) orientation.

[0168] Turning to FIG. 12, there is shown a diode laser integrated withthe applicator The diode laser (320) and spray applicator (322) aremounted on a common manifold (324). The manifold (324) contains a diodelaser pivot (326) and spray applicator pivot (328) for adjusting thealignment of each device with respect to the contact cleaning point onthe substrate (330). The cleaning manifold to connected to a multi-axisrobot (not shown) using a robotic mount (332). Connecting the manifoldto a multiaxis robot provides for any number of possible orientationsand angles as shown graphically. The diode laser is tunable to provideboth spot and broad-spectrum substrate heating—the robot provides thefocusing control for both the spray applicator and diode laser. Anotherfeature shown in the figure is a spin processor (334). The spinprocessor holds the substrate under vacuum (336) via a vacuum chuck(338). The substrate is spun at a rotational velocity of between 20 and5000 rpm. The laser cleaning manifold is scanned from the interior (asshown) to the perimeter of the substrate while the substrate is spinningbelow. Software is used to control the pressure, temperature and diodelaser process sequencing. One possible process using the presentembodiment involves decreasing propellant gas pressure while themanifold moves from the interior region (lowest centripetal force) tothe perimeter (highest centripetal force). Using this approach, theactual impact force (cleaning energy) of the stream is continuouslydecreased to compensate for the increasing centripetal force toward theperimeter—providing consistent cleaning energy across the entiresubstrate. Another process involves using the diode laser to preheat theentire substrate at a defocused distance above the substrate. The robotthen moves the entire applicator manifold to the focused position forintense lasing during cleaning. Finally, the photon-process is performedin a laser shielding box (340) to protect workers from exposure. Lasershielding may be constructed of many materials having suitable IR laserabsorbing/reflecting properties such as stainless steel or speciallycoated polymers and glasses.

[0169] The preferred wavelength for the diode laser used in the presentembodiment is about 940 nm. This wavelength is invisible to solid carbondioxide, allowing the snow spray cleaning operation to be performedsimultaneous with the lasing operation with no impact on eitherapplicator's performance. When used during snow cleaning, the nearinfrared laser operates predominantly on the substrate at the snowcleaning contact point and above—water vapor on and within atmosphereabove the contact point. Moreover, the snow spray is an excellentcoolant for the laser, preventing overheating of delicate substrates.

[0170] Combining cleaning with many industrial, semiconductor,microelectronic or disk drive manufacturing processes dramaticallyminimizes production times, superior process control, reducesconsumables costs, and eliminates the need for separate productionequipment such as soldering systems, stripping systems, curing ovens,thermal treatment systems, cool-down times and adhesive applicationsystems. Representative processes include:

[0171] cleaning to pretreat substrates prior to Laser microwelding ofmetals.

[0172] cleaning to pretreat substrates prior to application of adhesiveprior to Laser thermal cure.

[0173] cleaning to pretreat substrates prior to Laser soldering.

[0174] Laser-induced pyrolysis of coatings prior to ablation to reducestiction or adhesion.

[0175] Laser-induced excitation of boundary layer particles prior toablation to reduce intermolecular adhesive force.

[0176] Laser-induced heating during cleaning to prevent substratecooling.

[0177] Laser-induced heating prior to or following cleaning.

[0178] Laser drying of wet substrates prior to cleaning.

[0179] Laser removal of demarcations prior to cleaning.

[0180] Simultaneous cooling during soldering or joining to protectsensitive components from heat.

[0181] providing a rapid cooling following thermal joining.

[0182] Laser wire stripping and cleaning.

[0183] Advantages of this inventive embodiment include:

[0184] Multiple integration options—cleaning, cutting, soldering,joining curing and cooling.

[0185] Fiber optically coupled diode laser does far less collateraldamage as compared to Xenon Flash lamp-Pellet approaches such as in theBoeing FIashjet Approach.

[0186] Designed for microelectromechanical applications as compared tothe Boeing FlashJet approach (removal of coatings from aircraft wingsand bodies using a flashlamp and low velocity pellets). cleaning appliesto cleaning miniature surfaces such as head-gimbal assemblies (HGAs),quartz sensors, fiber optic lenses and quartz resonators.

[0187] Laser is generally line-of-sight cleaning for planar substratesunder highly controlled conditions, such as the Radiance approach, whilethe Diode Laser-approach can be applied to much more complicatedtopography with a generally less controlled approach. Diode lasers arenot wavelength specific and provide a general purpose intense heatsource. There is no need for focusing lenses, steering mirrors and thecustomized and complex and system/application-specific configurations(tooling) necessary for each type of substrate. The present inventionteaches the use of robotic focusing (working distance to substrate) tocontrol energy delivery.

[0188] Moreover, ultraviolet excimer lasers (KrF—248 nm), CO2, andNd:YAG lasers used by the Radiance system are used to produce photonflux to break bonds holding contaminants which are then swept away in alaminar gas flow stream above the substrate.

[0189] Compact size, high efficiency, low cost in mass production,high-power, fiber-coupled, diode laser arrays are a very goodalternative to CO₂ and Nd:YAG lasers in laser material processingapplications.

[0190] Coupling the systems to a 5-axis robot and software provides anarticulated and integrated production tool. Packaging this productiontool in a minienevironment provides a microcontamination-free productiontool. Multi-axis robots manage the substrates providing a completelyautomated (lights-out) production tool.

[0191] Combining LASER and dry cleaning technologies provides analternative to expensive and hazardous alternatives. This processeliminates water in the cleaning process that can be several 100 gallonsof expensive deionized water of approximately 2000 gallons used intypical semiconductor wafer production cycle. The present embodimentalso eliminates reprocessing and disposal costs, eliminates the need foralcohol drying and eliminates secondary reactions such as oxidation,ionic contamination, corrosion and bacterial growth.

[0192] The inventive embodiment removes contaminants that cannot beremoved using conventional snow cleaning techniques.

[0193] This inventive embodiment simultaneously heats a substrate duringcleaning which prevents a thin film of water ice from forming on thesurface of the substrate—encapsulating contaminants in a 300 psi tensilestrength sheet of ice. Furthermore, the substrate exits the process ator above ambient temperature which prevents re-deposition of vapor phaseand particulate contaminants.

[0194] Referring to FIG. 13, there is shown a robot-based integratedcleaning system and process simultaneously using the spray cleaning,laser heating and photoionization embodiments of the present invention.As shown in the figure, the substrate to be cleaned is a semiconductorwafer (342) mounted on a spin processor (344). The wafer is spun to aspeed of between 50 and 5000 rpm. The integrated cleaning tool comprisesa diode laser tense (346) which is fiber optically connected to ainfrared laser light generator and controller (not shown), a Snow sprayapplicator (348) which is connected coaxially connected to a generator(not shown), and a photoionization device (350) which connected to aphotoionization power supply (not shown). The integrated cleaning toolis further integrated on a common manifold (352) which is connected viaa robotic mount (354) to a cartesian robot (not shown). In Step 1 asshown, the integrated cleaning tool is robotically positioned above thesubstrate at the center of the substrate in the defocused position (356)wherein the diode laser beam is turned on and is irradiating a broadsection of the spinning substrate with infrared radiation (360). Thephotoionization device is also turned on and is irraditating a broadsection of the substrate with ionizing photons (362). In Step 2 asshown, the integrated cleaning tool is positioned in a focused positionat the center of the substrate (364). In this position, both the diodelaser beam (366) and photoionization beam (368) are in the highlyenergetic focused position. In Step 3 as shown, the substrate is scannedfrom the center (370) to the perimeter (372) any number of times toprepare the substrate for cleaning by drying, heating and ionizing thesubstrate. The temperature of the substrate may be preheated to anytemperature between 20 C. and 300 C. during this substrate preparationstep. A described herein, the use of the diode laser is varied and canbe for drying substrates, heating substrates, welding or joining. Inthis particular example, the laser is used to remove water and preheatthe substrate. In Steps 4 and 5 as shown, the spray applicator is turnedon (374) and all three devices are used simultaneously to clean thesubstrate any number of times by scanning from the center (376) to theperimeter (378) of the spinning substrate. In Step 6, the spray isstopped, leaving the diode laser and photoionizer on, whereby in Step 7the integrated cleaning tool is repositioned above the center of thesubstrate in the defocused position (380) using the robot (not shown).In Step 8, the integrated tool is scanned in the defocused position fromthe center (382) to the perimeter (384) of the spinning substrate toheat the substrate above ambient temperature. In Step 9, an infraredthermometer (386) is used to determine the temperature endpoint for Step8. The substrate is dry, clean, ionized and hot (388) following Steps 1through 9.

[0195]FIG. 14 shows a robotic cleaning workstation in accordance withthe present invention. As shown in the figure, Top View, the roboticcleaning workstation contains a multiaxis substrate transfer robot, suchas a Mitsubishi RV-M2, at the center and shown in four positions—loadingplatform position (390), cleaning platform position (392), inspectionplatform position (394) and offloading platform position (396). Dirtysubstrates are loaded into the loading platform position, a door isclosed (not shown), and the transfer robot picks up a substrate (398)from a fixture (400) located in the loading zone using an end-effector(402) such as a vacuum grip. The substrate is then transferred to thecleaning platform and placed onto a vacuum spin processor (404) that isintegrated to a cartesian robot (406) such as a Sony DeskTop Robot. Thecleaning applicator—a manifolded diode laser, spray applicator andphotoionizer (408)—is affixed to the cleaning robot and can be moved inany Cartesian direction X-Y-Z and the manifold can be rotated from anyoffset angle from 0 to 45 degrees from normal over the spinningsubstrate (410). The substrate cleaning process described above usingFIG. 13 is then performed. Following cleaning, the transfer robot picksup the substrate and transfers the substrate to the inspection platform(412). The inspection platform comprises an inspection robot (414) suchas a Sony Desktop Robot that is integrated with the OSSE surfaceanalysis sensor (416) embodiment. The inspection robot can be moved inany cartesian direction X-Y-Z and the inspection sensor can be rotatedfrom any offset angle from 0 to 45 degrees from normal over thesubstrate (418). The inspection sensor (416) is used to scan thesubstrate surface at a predetermined distance and surface inspectionpattern to discern molecular contamination remaining following cleaning.Alternatively, the inspection sensor may be a video camera for visualinspection of substrate features. Following inspection, data gatheringand analysis, the substrate cleanliness is either accepted or rejectedusing computer analysis software. Unacceptable cleanliness requires thesubstrate (418) to be recleaned. The transfer robot picks up thesubstrate and places the substrate onto a holding platform (420) if thecleaning platform (404) is occupied with another substrate, or returnsthe substrate back to the cleaning platform for recleaning. Followinginspection and acceptance, the transfer robot picks up the substrate(418) and transfers the substrate to the offloading platform (422) wherethe cleaned and inspected substrates (424) are collected for unloadingfrom the workstation.

[0196] Also shown in the Top View of FIG. 14 are the basic designfeatures of the workstation. These include a fully enclosed housing(426) constructed of stainless steel, acrylic or other suitbalematerials for using the present embodiments—1) safe-guarding workersfrom exposure to x-rays, laser radiation and carbon dioxide gas and 2)safe-guarding the cleaning environment within the enclosure fromexternal environmental elements such as moisture and particles. Theworkstation contains a vertical laminar flow ULPA filtration system(428) and a raised floor grating (430) for recirculating internalatmosphere. A computer console (432) is affixed to the outside of theworkstation for operator input and cleaning process output. The computerconsole contains a means for programming the various robots used in thepresent embodiment and for inputing cleaning and inspection criteria.Finally, a printer (not shown) may be integrated with the computerconsole for producing printed reports following each completed cleaningprocess cycle. Substrates are fed into the workstation using a loadingdock (434) which may contain a sliding door (not shown) and substratesare withdrawn from the workstation using an unloading dock (436) whichmay contain a sliding door (not shown).

[0197] Shown in the Side View of FIG. 14 are above-described andadditional features of the workstation. A lightstack assembly (438) isused to provide a visual operational status for the workstation (i.e.,Red-Operating, Green-Not Operating). All satellite systems including theCleaning System, Robot Control Systems, Fluids Management System,Accessory Control Systems and Input/Output and Power Control System arelocated within a control bay (440) located in the lower hemisphere ofthe workstation and isolated from the cleaning and inspection bay (442)located in the upper hemisphere of the workstation. Fluid input (gaseouscarbon dioxide), ventilation duct and electrical power connections aremade toward the rear of the control bay as shown in the figure. Anatmospheric management bay (444) located in the central hemisphere ofthe workstation integrates the floor grating (430) via a common ductingsystem (446) to an environmental control system (448) and the ULPAfilter system (428). As shown in the figure using arrows, the internalworkstation atmosphere is recirculated from the cleaning and inspectionbay (442) down through a raised floor grating (430), into theenvironmental control system (448), into the ULPA filter system (428)and back into the cleaning and inspection bay (442). The environmentalcontrol system (448) comprises a regenerating gas dryer (i.e., metaloxide) and heater (both not shown). Using a thermometer and humiditysensor (both not shown) located within the cleaning and inspection bay,the environmental control system maintains the cleaning and inspectionbay temperature and humidity at predetermined settings. Duringregeneration operations, the gas dryer is heated to 200 C. and drycarbon dioxide gas is used to purge moisture from the dryer which isvented from the workstation. Optionally, the ULPA filter system (428)may contain ionization bars (not shown) affixed to the downstream sideof the filter to provide internal ionization of the cleaning andinspection bay.

[0198] The entire cleaning process performed within the workstation isautomated and controlled using system software in combination with a PCor PLC, various electronic switches, digital controlled pressure andtemperature controllers, a robot, a photoemission inspection system andlaser system. The system software is written for Visual Basic operatingon a Windows NT and using an Allen Bradley PLC controller. The presentsystem software embodiment teaches in-situ correlation betweenphotoemission analysis and cleaning performance with automatic snowpressure and temperature adjustments. The system software also teachesan internet-based preventive maintenance code block within the softwareto perform remote system diagnostics and repair.

[0199]FIG. 15 shows the computer and software-based control systemarchitecture for automatically operating the various embodiments of thepresent invention. A main control system (450) comprising a centralcomputer system, programmable logic controller and software is used toprovide all input-output management of the cleaning process and system(452), inspection process and system (454), environmental control system(456), fluids management system (458) and robot controllers (460). Therobot controllers include the transfer, cleaning and inspection robots.The robots each have typically three components. For example thetransfer robot system (462) comprises 1) a teach pendant to teachpositions to the robot to execute the four pick and place operationswithin the workstation, 2) a robot controller to store taught positionsand to interface with the main control system (450) and 3) a multiaxisrobot containing an vacuum grip end-effector (464) or in the case of thecleaning and inspection robots—cleaning and inspection end-effectortools.

[0200] Operational software is used to manage and operate the varioussystems described herein. The computer software displays a graphicalinterface to the user, accepts inputs for a variety of processparameters and displays various system outputs.

[0201] Below are exemplary process inputs:

[0202] Cleaning Process Parameters:

[0203] EJTCR Injection Feedrate

[0204] Propellant Gas Temperature

[0205] Propellant Gas Pressure

[0206] Ionization Power Supply

[0207] Pulsed or Continuous Operation

[0208] Pulse Rate

[0209] Additive Injection

[0210] Additive Injection Feedrate

[0211] LASER System

[0212] LASER Pointer

[0213] LASER Power

[0214] Photoionizer System

[0215] Spin Processor System

[0216] Spin Processor Speed

[0217] Print Report (Yes/No)

[0218] Transfer Robot Parameters—Pick and Place Operational Recipes:

[0219] Load—Clean Positions

[0220] Clean—Inspect Positions

[0221] Inspect—Reject Positions

[0222] Reject—Clean Positions

[0223] Inspect—Unload Positions

[0224] Grip/Ungrip Positions

[0225] Transfer Speed

[0226] Cleaning Robot Parameters—Manifold Operational Recipes:

[0227] Starting Position(s)

[0228] Ending Position(s)

[0229] Focused Position(s)

[0230] Defocused Positions(s)

[0231] Offset Angles(s)

[0232] Scanrate

[0233] Number of Scans

[0234] Inspection Robot Parameters—Sensor Operational Recipes:

[0235] Starting Position(s)

[0236] Ending Position(s)

[0237] Focused Position(s)

[0238] Defocused Positions(s)

[0239] Offset Angles(s)

[0240] Scanning Rate

[0241] Number of Scans

[0242] Acceptance/Rejection Criteria

[0243] Print Report (Yes/No)

[0244] Below are exemplary process outputs:

[0245] Stream System:

[0246] Fluid Temperatures

[0247] Fluid Pressures

[0248] Fluid State (Gas/Liquid)

[0249] System Status

[0250] Robot Systems:

[0251] Cartesian Space Positions

[0252] Robot Status

[0253] Grip Status

[0254] Speed

[0255] Sequence

[0256] Environmental Control System:

[0257] Temperature

[0258] Humidity

[0259] Regeneration Sequences

[0260] Fluids Management System:

[0261] Temperature

[0262] Pressure Phase

[0263] Supply Level (Optical Sensor)

[0264] Inspection System:

[0265] Analysis and Results

[0266] Using the transfer robot system (462) and teach pendant (466),the user teaches the transfer robot the substrate transfer operationswhich move the substrate from the load position, through the cleaningand inspection positions (and holding position), and finally to. theunload position—called pick and place operations (468). Following this,the user inputs the leaning process parameters (452) and inspectionprocess parameters (454) given above into the computer, includingpass/fail analysis criteria (470) for the inspection process. Followingthis, the user has constructed a cleaning process recipe which can besaved as a unique process filename for future reference andrepeatability. The program may then be started (472), whereupon theentire cleaning process recipe, including robotics, cleaning andinspection criteria, is executed sequentially until completion (474).

[0267] Finally, the system software is designed with capability tocommunicate to a factory process management system through an Ethernetconnection (476). Moreover, the software is designed to allow a servicesupport technician to remotely diagnose system operation and functionover the internet (478).

[0268]FIG. 16 shows the cryogenic microabrasive surface finishingapparatus and process embodiment of the present invention. Machined ormolded polymeric substrates often contain plastic burrs around variousedges and surfaces. Removal of burrs using conventional deburring usingmicroabrasives does not always produce an acceptable surface because theburr tends to fold over during ablation. The present process provides ameans for producing ultrafme abrasive finishing by supercooling theburr, with respect to the substrate, thereby making the burr hard andbrittle. Impact by an abrasive under these conditions produces a cleanand fast separation because the burr temperature drops much faster thanthe substrate temperature.

[0269] The cryogenic abrasive finishing apparatus consists of a abrasivecleaning applicator (480) with the propellant gas supply (482)containing microabrasives fed down the coaxial delivery line (484).Dense snow particles are fed down a centrally located snow tube (486)from the EJTCR loop (488). The two streams are integrated at a distancefrom the abrasive cleaning applicator (480) using a tee connection(490). Any number of abrasives as shown may be employed in the presentembodiment.

[0270] The abrasive cleaning process is performed as shown and describedas follows. A substrate containing small edge burrs (492) is showeredwith an abrasive spray stream (494), with the propellant gas heaterturned off. Following this, the propellant gas heater is activated andthe microabrasive injection device (not shown) is deactivated—showeringthe substrate with a cleaning spray stream (496). The substrate (498) isnow finished and clean.

[0271] The present invention provides capabilities not found inconventional snow cleaning technology. The following is an cleaning andproduction application wherein the present invention is used to provideintegrated multiple cleaning operations during assembly, provide athermal curing process and dynamically alter snow spray cleaning energyduring application where the substrate contains mechanically sensitivefeatures that require the cleaning spray to have a lower spray pressurein one area and possibly an increased cleaning spray energy in otherareas. The following example is only one of many integrated substratecleaning, production and assembly operations possible using the presentinvention.

[0272] As shown in FIG. 17, the substrate—a small electronic chip or die(500)—is electrically connected to an electronic module (502) using anynumber of microscopic wires (504). The die is placed onto the electronicmodule and bonded into place. The spray cleaning processes of thepresent invention are used to clean the bonding surfaces of module (502)for the initial die placement and bonding operation. Following theinitial die placement, microscopic wires (504) are placed—joining theelectronic connections on the die (506) to the electronic connections onthe module (508). In the application, the interconnection bondingsurfaces are cleaned using the present invention prior to dispensing asmall droplet of a heat curing conductive adhesive (i.e., silver-filledepoxy). Following cleaning and adhesive placement, the small wires arerobotically placed into each epoxy solder joint Following this, thediode laser embodiment of the present invention is used to rapidly andthermally cure the epoxy joints. A final spray cleaning is performedusing the present invention to remove any residual particles followingdie bonding, adhesive placement, wire bonding and curing operations andprior to lid placement. The spray pressure is dynamically controlled toproduce a much lower spray pressure in the regions near the wires. Asshown in the figure, the spray pressure is decreased from 80 psi (510),to 50 psi (512) and finally to 30 psi (514) as the spray applicator(indicated as arrows) approaches the mechanically sensitive wire bondingareas.

1. A dense fluid spray cleaning apparatus comprising a gas supply forproviding a predetermined amount of a dense liquid to an enhancedjoule-thompson condensation reactor and for providing gas to apropellant generator, a premix chamber for receiving solid particulatefrom the enhanced joule thompson condensation reactor and heated gasfrom the propellant generator, a mixing chamber for receiving the solidparticulate and propellant and producing a stream containing the solidparticulate.